This makes sense. A revised version of this patch, moving qemu_mknodat from 9p-util to osdep and os-posix, is attached below. I'd appreciate any feedback from those looped in here, so that the context isn't lost before resubmitting as a v5 patch, especially since this is starting to touch files outside of 9p.
From c9713c87163da7c96b5357d0d85ac318ae3d3051 Mon Sep 17 00:00:00 2001
From: Keno Fischer <
keno@juliacomputing.com>
Date: Sat, 16 Jun 2018 20:56:55 -0400
Subject: [PATCH] 9p: darwin: Implement compatibility for mknodat
Darwin does not support mknodat. However, to avoid race conditions
with later setting the permissions, we must avoid using mknod on
the full path instead. We could try to fchdir, but that would cause
problems if multiple threads try to call mknodat at the same time.
However, luckily there is a solution: Darwin includes a function
that sets the cwd for the current thread only.
This should suffice to use mknod safely.
This function (pthread_fchdir_np) is protected by a check in
meson in a patch later in tihs series.
Signed-off-by: Keno Fischer <
keno@juliacomputing.com>
Signed-off-by: Michael Roitzsch <
reactorcontrol@icloud.com>
[Will Cohen: - Adjust coding style
- Replace clang references with gcc
- Note radar filed with Apple for missing syscall
- Replace direct syscall with pthread_fchdir_np and
adjust patch notes accordingly
- Move qemu_mknodat from 9p-util to osdep and os-posix]
Signed-off-by: Will Cohen <
wwcohen@gmail.com>
---
hw/9pfs/9p-local.c | 4 ++--
include/qemu/osdep.h | 10 ++++++++++
os-posix.c | 34 ++++++++++++++++++++++++++++++++++
3 files changed, 46 insertions(+), 2 deletions(-)
diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index a0d08e5216..d42ce6d8b8 100644
--- a/hw/9pfs/9p-local.c
+++ b/hw/9pfs/9p-local.c
@@ -682,7 +682,7 @@ static int local_mknod(FsContext *fs_ctx, V9fsPath *dir_path,
if (fs_ctx->export_flags & V9FS_SM_MAPPED ||
fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) {
- err = mknodat(dirfd, name, fs_ctx->fmode | S_IFREG, 0);
+ err = qemu_mknodat(dirfd, name, fs_ctx->fmode | S_IFREG, 0);
if (err == -1) {
goto out;
}
@@ -697,7 +697,7 @@ static int local_mknod(FsContext *fs_ctx, V9fsPath *dir_path,
}
} else if (fs_ctx->export_flags & V9FS_SM_PASSTHROUGH ||
fs_ctx->export_flags & V9FS_SM_NONE) {
- err = mknodat(dirfd, name, credp->fc_mode, credp->fc_rdev);
+ err = qemu_mknodat(dirfd, name, credp->fc_mode, credp->fc_rdev);
if (err == -1) {
goto out;
}
diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index d1660d67fa..f3a8367ece 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -810,3 +810,13 @@ static inline int platform_does_not_support_system(const char *command)
#endif
#endif
+
+/*
+ * As long as mknodat is not available on macOS, this workaround
+ * using pthread_fchdir_np is needed. qemu_mknodat is defined in
+ * os-posix.c
+ */
+#ifdef CONFIG_DARWIN
+int pthread_fchdir_np(int fd);
+#endif
+int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev);
diff --git a/os-posix.c b/os-posix.c
index ae6c9f2a5e..95c1607065 100644
--- a/os-posix.c
+++ b/os-posix.c
@@ -24,6 +24,7 @@
*/
#include "qemu/osdep.h"
+#include <os/availability.h>
#include <sys/wait.h>
#include <pwd.h>
#include <grp.h>
@@ -332,3 +333,36 @@ int os_mlock(void)
return -ENOSYS;
#endif
}
+
+/*
+ * As long as mknodat is not available on macOS, this workaround
+ * using pthread_fchdir_np is needed.
+ *
+ * Radar filed with Apple for implementing mknodat:
+ * rdar://FB9862426 (
https://openradar.appspot.com/FB9862426)
+ */
+#ifdef CONFIG_DARWIN
+
+int pthread_fchdir_np(int fd) API_AVAILABLE(macosx(10.12));
+
+int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev)
+{
+ int preserved_errno, err;
+ if (pthread_fchdir_np(dirfd) < 0) {
+ return -1;
+ }
+ err = mknod(filename, mode, dev);
+ preserved_errno = errno;
+ /* Stop using the thread-local cwd */
+ pthread_fchdir_np(-1);
+ if (err < 0) {
+ errno = preserved_errno;
+ }
+ return err;
+}
+#else
+int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev)
+{
+ return mknodat(dirfd, filename, mode, dev);
+}
+#endif
--
2.34.1